[6-15N]-2'-DEOXYADENOSINE WAS CONVERTED TO [6-15N]-6-N-BENZOYL-2'-DEOXYADENOSINE BY THE METHOD OF JONES AND CO-WORKERS TO GIVE A 62 % YIELD (SCHEME 2). THIS MATERIAL WAS THEN TREATED WITH DIMETHOXYTRITYL CHLORIDE IN PYRIDINE. THE REACTION WAS STIRRED FOR 3 HOURS AND THEN QUENCHED WITH METHANOL (77% ISOLATED YIELD). IT WAS EVENTUALLY FOUND THAT THE YIELD OF THE TRITYLATION REACTION COULD BE RAISED (AND MORE CONSISTENT) IF FRESHLY CRYSTALLIZED DIMETHOXY TRITYL CHLORIDE IS USED (WHITE POWDER UNLESS EXPOSED TO AIR). THE 1H NMR FOR THE [6-15N]-6-N-BENZOYL-5'-DIMETHOXYTRITYL-2'-DEOXYADENOSINE IS SHOWN IN PANEL 1, AND IT CLEARLY SHOWS THE 15N-H DOUBLET CENTERED AROUND 8.70 PPM. CONVERSION OF THE 3' HYDROXYL TO THE H-PHOSPHONATE WAS ACCOMPLISHED USING 2-CHLORO-4H-1,2,3-BENZADIOXO-PHOSPHORIN-4-ONE, A COMMON PHOSPHITYLATING AGENT (CRUDE YIELD 96%). THE PROTON COUPLED 31P NMR IS ILLUSTRATED IN PANEL 2. THE 3-BOND COUPLING OF THE 3' PROTON WITH THE PHOSPHORUS IS CLEARLY DISCERNIBLE.